This invention relates to fluid filters and, more particularly, to improved pressure relief valve assemblies and antidrain back (ADB) valves for spin-on, disposable, oil filters.
Spin-on, disposable, oil filters are used with internal combustion engines to filter out small particulate matter which would otherwise abrade moving engine parts. After a recommended time interval, the old filter is replaced with a new filter and is therefore considered disposable.
Such a filter has an outer casing, a filter element disposed within the casing, an end member fixed at one end of the casing, a pressure relief valve assembly, which allows by-pass of the filter element, when desired, and an ADB valve. Plural inlet ports and a central outlet port are provided in the end member to allow oil to circulate through the filter element. The central outlet port is usually threaded for "spin-on" mounting of the filter to an engine.
Conventional pressure relief valve assemblies are known to be of the metal or plastic types.
More particularly, as described in U.S. Pat. No. 3,473,664, issued to HULTGREN, and shown in FIG. 1 herein, a known metal pressure relief valve assembly 10 includes an upper housing 12, against which a filter element 14 usually abuts, and a lower housing 16. The lower housing 16 includes oil inlet holes 18. The upper housing 12 retains a compression spring 20 which urges an elastic piston 22 downwardly via a metal piston support 24 into a seated position over the inlet holes 18 formed in the lower housing 16. The metal piston support 24 includes an upright annular flange 25 which receives radially outward the compression spring 20.
When, e.g., the filter element 14 is full of contaminants, oil pressure at the oil inlet holes 18 increases and exerts an upward force which overcomes the force on the piston 22 and piston support 24 exerted by the compression spring 20. If a pressure threshold is surpassed, the piston 22 is unseated, thereby enabling oil to by-pass the filter element 14 and leave the oil filter 26 through the center tube 28 and a central outlet 30.
It is known that these metal pressure relief valves suffer from several drawbacks. First, a high degree of dimensional variability is necessitated by the numerous parts, which leads to exceeding desired relief valve opening pressures. Second, relatively high production costs result due to the number of parts, the cost of metal and the need to fixedly connect the upper and lower housings by automation while they are under spring pressure. Finally, sealing reliability over time is less than desired.
Plastic pressure relief valve assemblies are also known. A typical plastic assembly is described in U.S. Pat. No. 3,156,259, issued to HAVELKA et al. and shown in FIG. 2 herein. The assembly 48 is shown including a metal valve plate 50 which is urged into a seated position against a flanged portion 52 of a valve body 54 by means of a compression spring 56. The spring 56 is disposed between the valve plate 50 and hooked extensions 57, 58 which are integrally formed with the valve body 54. The flanged portion 52 is also integrally formed or molded of plastic material with the valve body 54. The valve plate 50 is essentially an annular planar member having an inner, upstanding flange portion 59 which receives radially outward the compression spring 56.
Although HAVELKA et al. suggests the need for only a metal valve plate 50, the HAVELKA et al. plastic relief valve requires, in practice, both a rubber piston and a metal piston support as evidenced by subsequent U.S. Pat. Nos. 3,589,517, issued to PALMAI and 4,028,243, issued to OFFER, which incorporate the HAVELKA et al. valve design along with a rubber piston. 0f course, requiring both a piston and piston support increases raw mterial and assembly costs. Further, these plastic relief valves, like the metal valves discussed above, require a compression spring which must be assembled on the valve body.
Further, each of the two prior art types of pressure relief valve assemblies described above requires a separate means for retaining a coil spring, uses a spring urging both a piston and piston support into sealing relation and is susceptible to seal deterioration during operation.
Of related interest is U.S. Pat. No. 3,231,089 showing a one-piece, molded rubber, combined pressure relief/ADB valve. U.S. Pat. No. 4,045,349 also shows a combined pressure relief/ADB valve structure.
Overall, it is desirous that a pressure relief valve assembly be capable of the lowest cost manufacture and be capable of efficient sealing properties. For example, a design which eliminates the need for a separate compression spring or retainer therefore is desired. In addition, having flexibility in choosing the materials and structural design of the assembly is preferred to being limited to a particular type and configuration. Finally, it is desirous that a valve be capable of relatively quick and easy automated assembly requiring no welding, brazing, or soldering.
As noted above, filters also include ADB valves. An ADB valve prevents gravity induced draining of the filter which would otherwise occur when the engine is not operating. This is a desirable feature since a drained oil filter would otherwise momentarily interrupt circulation of oil when the engine resumes operation.
Again referring to FIG. 1, a conventional ADB valve 38 includes a rubbery, annular flap 40 and a corresponding metal spring 42 which overlie the plural inlet ports 44 of an end member 46. The ADB valve 38 opens in the direction of arrows "A" in response to oil flowing into the filter 26 through the inlet ports 44. When oil flow ceases by virtue of the engine shutting down, the ADB valve 38 returns to its normal seated position against the end member 46 to prevent oil within the filter 26 from draining out through the inlet ports 44.
As described above, ADB valves conventionally include two components which must be separately formed and assembled in the filter. It is always desired, if possible, to minimize component part assembly steps and overall production costs and time. As a result, a simpler ADB valve is desired.
Although the relevant art described above eliminates some of the problems inherent in the oil filter art, a need exists for a pressure relief valve assembly, an ADB valve and an oil filter incorporating same that is more consistent in operation and cost effective to produce.